This invention relates to making armatures for dynamo-electric machines such as motors and generators. Although the invention will be described primarily in the context of its application to electric motor armatures, it will be appreciated that it is equally applicable to rotating rotors in general which are wound with wire for conducting electric current. For convenience, all such rotors are referred to herein as armatures. Also, although the invention will be described primarily in the context of flyer type armature coil winders, it will be understood that the invention is equally applicable to winders that employ other types of coil wire dispensing members such as the apparatus shown in commonly assigned, co-pending applications Ser. Nos. 07/738,199 and 07/742,629.
With reference to accompanying FIG. 1, finished armatures 10 wound with wire 12 in coil receiving slots 14 of a lamination stack 16 need to be precisely balanced prior to their final operational use. This avoids mechanical malfunctioning, and also guarantees the integrity of the armature, together with that of other components which are assembled in the environment where the final operational use occurs.
It is common practice to use automatic balancing machines at the end of an armature production line to determine the amount of unbalance produced during the processing stages and to correct for this unbalance by adding or removing masses on certain parts of the finished armature. The most common technique for automatic balancing of armatures removes masses by milling one or more grooves in the outer circumferential surface of the armature stack 16.
Unbalance (requiring balancing as described above) may be the result of unbalances present in the mass of stack 16, in the mass of shaft 18, in the mass of commutator 19, and also in the overall disposition of these masses as a result of the operations required to assemble them to form the armature. Unbalance of the armature can also result from the operational steps required to wind the coils of wire 12 in the slots 14 of stack 16. Although the disposition of the coils (and their number of turns) around the armature is theoretically correct for avoiding unbalance, practice has shown that the winding process can introduce unbalance.
In order to reduce the need for or the required extent of a final balancing step in the manufacture of armatures, it is an object of this invention to reduce or substantially eliminate unbalance which may otherwise result from the coil winding operation.
Formation of armature coils requires simultaneous winding of two wires in two pairs of slots which are symmetrically opposite one another as shown in accompanying FIG. 2. For example, coil 20 is wound in slot pair 22, 23 symmetrically opposite to coil 21 which is simultaneously wound in slot pair 24, 25.
One of the fundamental production specifications for winding armatures usually requires winding symmetrically opposite pairs of slots (such as those referenced above) with the same number of turns of wire. As has been mentioned, this creates a theoretical basis for avoiding unbalance, although, as will be more fully described below, in practice during winding various factors can cause unbalance.
Armatures of the type shown in accompanying FIG. 1 are frequently wound with a flyer type winder, although other types of winders (e.g., those shown in above-mentioned application Ser. Nos. 07/738,199 and 07/742,629 (both of which are incorporated by reference herein)) are also known and are subject to the same problems and solutions discussed herein. As shown in accompanying FIGS. 3 and 4, the typical flyer type winder includes two opposite flyers 30, 31 which can rotate around respective axes 32, 33 so that each of them dispenses an associated wire 34, 35 coming from a wire spool 36, 37 into a respective pair of coil receiving slots 38, 39 and 40, 41 aligned with prepositioned winding forms 42, 43. The winding forms are required to guide each wire into the coil receiving slots as the wire leaves the associated flyer. The wires required to wind the coils, prior to reaching the flyers from the wire spools, pass through respective tensioner devices 46, 47 which are supposed to guarantee that predetermined tensions are maintained on the wires during the various operations required to wind and form the leads of the armature. The two flyers 30 and 31 rotate at the same time so that each of them forms a coil in respective pairs of slots which are symmetrically disposed on opposite sides of a central transverse axis 80 of the armature. Flyers 30 and 31 are driven by independent motors 44, 45, which are controlled to rotate in unison so that both flyers reach, as precisely as possible, similar predetermined angular positions in time. In particular, the two flyers start and terminate rotation at the same time so that both coils are wound simultaneously with the same number of turns.
At any given instant of time during winding, a difference between the tension of the wires being wound by their respective flyers can result in different elongation of the wires. In a comparison between the two flyers, which are winding opposite coils at the same time, this leads to supplying in certain instances different masses of wire into symmetrically opposite pairs of slots of the armature (such as those shown in FIG. 4). This has an unbalancing effect on the armature. In addition, a coil wound with higher tension will have more compact turns, which influences the radial disposition of its mass (e.g., in relation to the central longitudinal axis 82 of the armature). This also contributes to unbalance if variations of this type exist between the opposite coils being formed at the same time by the two flyers.
The foregoing considerations can be further illustrated with the aid of accompanying FIG. 5, in which certain features are somewhat exaggerated. The wires relating to a few coil turns for respective opposite coils 20, 21 are shown. The turns of coil 21 are wound with higher tension, which subjects the wire to a greater amount of elongation for the same number of turns. This causes coil 21 to have less wire mass and to be more compact toward the central longitudinal axis 82 of the armature than coil 20. It should be appreciated that the formation of the overall coils of the armature requires a progressive build-up of wire turns and also of different coils. Later-wound turns and coils surmount earlier-wound turns and coils so that the later-wound material is farther away from central axis 82. As a result of this overlying or overlapping, the presence of an internal coil which is less compact tends to amplify the unbalance because it also affects the mass disposition of successive coils which will be positioned farther away from the central longitudinal axis 82 of the armature.
In view of the foregoing, it is an object of this invention to reduce or substantially eliminate the unbalance of an armature that may be due to the coils wound on the armature.
It is a more particular object of this invention to reduce or substantially eliminate the previously described differences which may exist between two coils wound simultaneously on an armature by two flyers or other wire depositing elements, so that unbalance introduced during the winding process of an armature can be reduced or substantially eliminated.